The invention relates to a thin-film magnetic head comprising a substrate, a first transducing element and a second transducing element, which elements are located at different distances from the substrate, and three substantially parallel extending magnetically conducting flux guides for magnetic cooperation with said elements, a non-magnetic read gap adjacent to a head face extending between the first flux guide and a second flux guide and a non-magneti write gap adjacent to the head face extending between the second (shared) flux guide and the third flux guide, said gaps, viewed from the substrate, being situated one above the other.
A magnetic head of this type is known from JP-A 62-145527 (herein incorporated by reference). The known magnetic head is a combined write/read head having a contact or head face, which is manufactured in accordance with a thin-film technique and comprises three flux guides, viz. two outer flux guides and one central (shared) flux guide. A transducing or inductive element in the form of an electric conductor and a non-magnetic layer are provided between one of the outer flux guides and the central flux guide, the non-magnetic layer defining a write gap. The known magnetic head thereby forms a write portion, for writing information on a magnetic medium for example, a magnetic tape moving along the contact face when the electric conductor is controlled. A transducing or magnetoresistive element, a bias winding and a non-magnetic layer defining a read gap are provided between the central (shared) flux guide and the other, outer flux guide. The portion of the known magnetic head formed thereby is a read portion for reading information on the medium moving along the contact face.
In the known magnetic head, the central flux guide is a shared flux guide which forms part of a magnetic yoke of the write portion as well as of the magnetic yoke of the read portion of the magnetic head. It is known that a write gap may function as a read gap when information is being read. This phenomenon is utilized in a structure in which information is written and read by one and the same inductive element. However, in the write/read magnetic head known from said Japanese Patent publication, the write gap functioning as a read gap has the detrimental result that a part of the magnetic flux of the passing medium which is opposite the write gap is guided towards the magnetoresistive element via the shared central flux guide. As a result, extra magnetic pulses are introduced into the magnetoresistive element in the case of, for example, a medium comprising digital information, which pulses interfere with the magnetic pulses guided towards the magnetoresistive element via the read gap, which perturbs the signal to be measured and detrimentally influences the signal-to-noise ratio.
The detrimental phenomenon described above, which occurs in the known magnetic head during operation, is elucidated as follows. If it is assumed that a small magnetized area on a recording medium, for example, a magnetic tape is present just in front of the write gap, this area can be considered to be an almost ideal flux source due to the low permeability of the medium. A part of the flux, which is dependent on the distance from the size of the write gap, will enter the write portion via the outer flux guide adjacent to the write gap and will leave the write portion via the central flux guide, or vice versa. The greater part of the magnetic flux entering the write portion returns to the contact face via the magnetic yoke of the write portion. However, since the outer flux guide adjacent to the read gap extends parallel to and at a short distance from the shared central flux guide, a certain part of the flux taken up in the write portion will cross over to the last-mentioned outer flux guide. This part of the flux subsequently traverses the sensitive magnetoresistive element and then returns mainly via the central flux guide to the magnetized area on the medium. The flux portion which directly crosses over to said magnetic area from the outer flux guide adjacent to the read gap is negligibly small due to the relatively large distance between this flux guide and the magnetic area and due to the exponential character of the distance losses then occurring. Dependent on the direction of movement of the medium, the part of the flux traversing the magnetoresistive element gives rise to an extra pulse before or after the main pulse which results from reading said magnetized area by the magnetic head.
Measurements and calculations which have been carried out on magnetic head structures related to the known magnetic head show extra pulses with an amplitude ranging between 5 and 15% of the amplitude of the main pulse, dependent on the thickness of the central flux guide and on the permeability of the soft-magnetic material of the flux guides.
Moreover, when information is being written, the quantity of magnetic flux generated by the inductive element and guided towards the magnetoresistive element via the shared flux guide may be so much that the magnetoresistive element is destabilized, which may considerably reduce its sensitivity.